PS 1.2a

1. PS 1.2a Hybrid Active-Passive Rotor Systems for Vibration and Performance Principal Investigators Kon-Well Wang Diefenderfer Chaired Professor Mechanical Engineering Tel : (814) 865-2183 Edward Smith Professor Aerospace Engineering Tel : (814) 863-0966 Graduate Student Jun-Sik Kim 2005 RCOE Program Review May 2, 2005

2. Background • The rotorcraft industry is aggressively pursuing successful and cost effective active control systems to reduce vibration. • Blade loads are design constraints for primary control and life cycle. • Actuator authority present major technical barrier.

3. Vibration UMd, PSU, et al. g’s w/ control w/Control improved actuators V Blade loads hybrid design approach f’s w/ control w/Control Penn State (1996 - ) Problem Statement and Task Objective How do we design effective active vibration/blade loads control systems for future rotorcraft ? V Objective: To address the critical issues and advance the state- of-the-art of rotorvibration suppressionand blade loads reduction through combining the two approaches • High authority PZT actuators • Effective hybrid vibration/blade loads control system • Design high authority actuator system • Large stroke and force and low electric power • Design active controller together with passive parameters • Re-configuration of passive structure (m, GJ, EI, etc)

4. 600 7 500 Haero* Haero* 400 T* 300 1 1 5 3 200 Small scale blade chord T* 100 0 0 5 10 15 20 25 3 Chord (in) MD900 blade chord Piezoelectric Actuator Scaling Performance as Blade Size Haero* ~ c2R T* ~ c3 • Aerodynamic Moment and Block Torque non-dimensionalized with small scale values

5. Boeing 2xFrame Actuator 2003 Full Scale Whirl Test Results (SPIE 2004, Straub et. al) Flap deflection vs. rotor speed multiple • Modified MD 900 bearingless rotor • 3~3.5 degrees in hover (450V) Large rotor test stand (LRTS)

6. Technical Barriers and Solution Idea • 1) High active authority and low electric power of actuator for actuator/flap coupled systems • Resonant Actuation System (RAS) • 2) Multiple trailing edge flap configuration to utilize the resonance actuation system • Vibration and blade loads reductions Resonance Actuation System(RAS) Multiple Trailing Edge Flaps

7. Technical Evolution Nature’s Flight Actuators

8. Summary of 2001 - 2003 Accomplishments Active authority enhancement of PZT actuator • Circuit with negative capacitor and active inductor/blocking filterswas explored to reduce electric power (2001) • New concept to enhance the active authority of PZT actuators was developed and evaluated on PZT benders, stacks, and tubes (2002) • Full-Scale PZT tube / R-L-C circuit system was experimentally realized and evaluated (2003) • Aeroelastic flap/torsion model for composite rotor blade was developed (code validation, 2001) • Refine control algorithm of hybrid design was developed to achieve both blade loads and vibration reductions with minimum control efforts (2002) • Multiple trailing edge flap configurations with RAS was explored to reduce the vibration (2003) Blade loads and vibration control via TEF

9. 2004 Review Team Comments • The task made good progress and made good responses to the last year suggestions. • The task deals with vibration only and it is suggested to check noise aspect of the concepts. - Other Research is focused on trailing edge flaps for noise reduction. (e.g. Prof. Friedmann at Univ. of Michigan has 2005 AIAA and AHS papers on this subject). - Researchers in industry (e.g. Straub et al) have also examined this idea. - A thorough investigation of noise reduction was considered beyond the scope of the present investigation. • The review team is curious about drag penalty of TEF? - This is an important question. - Increments in section drag are modeled in the airload calculation - Primary penalties are for flap deflections near transonic Mach number (adv side) and negative deflections at high angles of attack (retreating side) - Proper control law design can mitigate these penalties (Zhang, Smith, Wang, 2000)

10. Performance Enhancement Retrofit Design at 0.15 Retrofit Design at 0.30 Flap Down Flap Up • Large flap deflections may occur around 90° and 270° azimuths, which can cause aerodynamic penalties - stall and separation

11. Performance Enhancement • Modified objective function and control algorithm : The active flap deflections at certain time history :Weighting factor

12. Performance Enhancement Retrofit design at advance ratio of 0.30 Retrofit with constraints Retrofit • Active Flap deflections around 270° azimuth are reduced to within 2 degrees

13. Performance Enhancement Hybrid design at advance ratio of 0.15 Hybrid with constraints Hybrid • Active flap deflections around 90° azimuth are reduced from more than 6 degrees to about 2 degrees

14. Summary of Accomplishments in 04/05 Analysis and Experiment of Piezoelectric Resonant Actuation Systems • Analysis is performed to explore the feasibility of a resonant actuation system (RAS) • Dynamic characteristics of a RAS is examined via perturbation method (forward flight) • Power consumption of a RAS is explored • Experiment of a RAS with adaptive feed-forward controllers – Bench Top Test • A voltage signal function is derived from the analytical model and implemented using Matlab/dSPACE • A phase controller, so called ‘phaser’, is implemented to track the phase variation near a resonant frequency • Actuator amplification mechanism of a RAS is modified to improve the dynamic performance – 6.0 degrees are achieved

15. Tune to Operating Frequency via Mechanical Tuning Typical Trailing Edge Flap Deflections Required authority 3,4,5/rev 3/rev 5/rev 4/rev Broaden and Flatten via Circuit design Frequency, Hz Actuator stroke Three Small Actuators • Single flap  Three small flaps frequency 3/rev 4/rev 5/rev IDEA – Actuator authority enhancement Resonance Actuation System • Resonance can be utilized to improve the actuator authority • Electric network can help to broaden and flatten the resonant driver effect Single nominal actuator (baseline) • Baseline - Small active authority over operating range • Increase authority via mechanical tuning and electrical tailoring • May not cover the entire range of operating frequencies

16. Multiple TEF w/ RAS RAS Resonance Actuation System Application Resonance Actuation System 1) PZT Actuator 2) Trailing Edge Flap (Aerodynamics) 3) Electric Circuit Mechanical Tuning • Amplification mechanism • Mass moment of inertia of TEF Electric Network • Inductor: tune to operating frequency (e.g., 3,4,5/rev) • Resistor: flatten the resonant peak • Negative capacitor: broaden the resonant driver effect

17. Hover Forward Flight M K • Hover: stiffness is constant • Forward flight: stiffness is varying along the azimuth • Periodic coefficient due to 1/rev aerodynamic forces • Time-varying characteristics of actuation system will be discussed further Mechanical Tuning Tuning mass: Mtune Tube actuator: Kp,Mp Flap hinge • Resonant frequency : 2 =K / M • Tuned to the operating frequency (e.g. 3, 4, 5/rev) • Tuning parameter: Tuning mass, Amplification ratio Aerodynamic loads: Kf   Tuning mass: Mtune Trailing-Edge Flap: Mf Amplification mechanism,  = Am , Am=llever / loffset (e.g. Am=5 will provide 5:1 amplification)

18. Active authority: The circuit canbroaden and flatten the resonant effect of the tuned system and still maintain high authority Inductor: tune to operating frequency (e.g., 3/rev, 4/rev, 5/rev) Negative capacitor: broaden the resonant driver effect Resistor: flatten the frequency response around the resonant peak Broaden and Flatten via Circuit design Actuator authority enhancement at tuned frequency via Mechanical tuning Problem: It is hard to control (Resistor, Inductor) • Bruneau et al.(1999) • Tang and Wang (2001) • Behrens et al. (2001). Phase plot frequency Electrical Tailoring Resonant frequency Actuator stroke Operating frequency: 3,4,5/rev • Phase variation near resonant freq. • Need to design controller to track phase variation • Developed and tested in this year’s effort

19. Perturbation Method in Forward Flight • Time-varying characteristics of actuation system • Equations of motion of a coupled system w/o circuitry • Primary resonance at = (resonant frequency in hover) • Resonances due to time-varying characteristics at 2 = 2, (1)2, (2)2 • Flap response qt includes other harmonics: (1), (2), … • For example, if =4, then qt includes 2,3,4,5,6/rev harmonics : Theodorsen’s theory for trailing edge flap • Normalized equations for the purpose of perturbation • Perturbed solution up to 2

20. Advance ratio 0.35 Actuation system with circuitry Hover Advance ratio 0.15 Operating frequency, 4/rev, 26.6Hz Frequency Responses in Forward Flight Actuation system w/o circuitry • RAS in hover • The actuator authority is significantly increased from 1.25 degree to 4.5 degree • Flat and wide shape near the resonant frequency (approximately 8 Hz). • RAS in forward flight • Main characteristics of the RAS (high authority with wide bandwidth) are achieved in forward flight • Influence of advance ratios to the major resonant frequency is not significant • RAS can be applied to forward flight as well as hover

21. Flap Time Histories in Forward Flight (=0.35) Resonant Actuation System Nominal actuation system • 4/rev voltage signal input • 4/rev harmonic component is increased from 1.5 to 3 degrees • Need to develop controller to resolve the side effects

22. Summary of Accomplishments in 04/05 Analysis and Experiment of Piezoelectric Resonant Actuation Systems • Analysis is performed to explore the feasibility of a resonant actuation system (RAS) • Dynamic characteristics of a RAS is examined via perturbation method (forward flight) • Power consumption of a RAS is explored • Experiment of a RAS with adaptive feed-forward controllers – Bench Top Test • A voltage signal function is derived from the analytical model and implemented using Matlab/dSPACE • A phase controller, so called ‘phaser’, is implemented to track the phase variation near a resonant frequency • Actuator amplification mechanism of a RAS is modified to improve the dynamic performance – 6.0 degrees are achieved

23. Phase plot Feed-Forward Controller for RAS Voltage Signal Function emulating of electric network • Electric network is realized via “Voltage Signal Function” which is derived from the coupled piezoelectric equations • The phase angle  is adaptively corrected through the feedback of the output signal Adaptive “phaser” to track the phase variation

24. Experiment Set-up • 8 inch PZT tube, 12 inch flap (inertia only) • Amplification ratio: 5 (current), 15 (future) • Mechanical tuning to 4/rev (26.6Hz)

25. Operating frequency 3.5 w/o voltage signal function w/ voltage signal function Bench Top Test Results Frequency Response Phase Control at 24 Hz • Actuator authority at the tuned frequency (26.6Hz) • Increases about 3.5 times when compared to the static deflection (which would be produced by nominal actuation system) with 8 Hz bandwidth • The phase near a resonant frequency varies • Implemented adaptive controller is able to accurately follow the reference

26. Demonstration of RAS Resonant Actuation System with simulated aerodynamic loads & improved amplification mechanism • Full-scaled PZT tube actuator fabricated (Jose Palacios and Edward Smith, 2005) • PZT tube is 4 inches long • Simulated aerodynamic loads • Two springs (80 lb/in total) • Applied voltage: 2250 Volts • Mechanical tuning: 33.3 Hz for MD 900, 5/rev • Flap deflections with simulated aerodynamic loads • 12 inches flap, 400 RPM •  6.0 degrees are achieved at the operating frequency • Nominal actuation authority is 0.2 degrees: 30 times increases Mechanically tuned actuator w/o voltage signal function Test with voltage signal function is scheduled in near future

27. Planned Efforts in 2005 • Controller design for flap responses in forward flight • Reduce the side effects due to time-varying characteristics • Investigate the characteristics of a RAS further • Continue the test of a RAS with a voltage signal function • Nonlinear characteristics of a RAS Controller for side effects Characteristics of a RAS

28. Summary of Overall Accomplishments Objective: To advance the state-of-the-art of rotor vibration suppression and blade loads reduction through combining the two approaches • Development of actuation systems for active flap rotors • A resonant actuation system (RAS) was developed • Bench top testing of full-scaled actuation system • Dynamic characteristics of a RAS in forward flight were explored • Actuator amplification mechanism of a RAS is modified to improve the dynamic performance • High authority PZT actuators • Effective vibration/blade loads control system • Development of analytical tool for rotor analysis • Free-wake for main rotor, unsteady aero and finite wing effects for flaps • Active load controls via dual flap (blade loads reduction) • Vibration reduction via multiple trailing edge flaps controlled by resonant actuation system

29. Future Work • Hover or wind tunnel test of a RAS • Active load controls for Heavy Lift Helicopters • Dual flap configuration together with RAS for light weight rotors • Damage detection using active flaps in forward flight • Active interrogation could be combined with active loads control Active load controls via dual-flap Damage identification using trailing edge flaps 1. Deformed blade 2. Straightened blade

30. External Interactions, Leveraging and Technology Transfer • Have had discussions with • US Army AFDD (Mark Fulton, smart rotor testing, resonant actuator and circuit concept, flap aspect ratio effect) • Boeing (Friedrich Straub, actuator requirements) • Sikorsky: visited (A. Bernhard, feasibility of multiple-flap configuration) • U. Maryland (I. Chopra et. al, hinge moments) • U. Michigan (P.P. Friedmann, auto-weight control)

31. External Interactions, Leveraging and Technology Transfer • Novel, high authority flap actuation concepts using single crystal stacks – SBIR (Small Business Innovation Research) • Invercon and PennState • Buckling beam actuator together with RAS – high actuation authority

32. Publications and Presentations • Jun-Sik Kim, Edward C. Smith and Kon-Well Wang, "Active loads control of composite rotor blade via trailing edge flaps", 44th AIAA/ASME/ASCE/AHS/ASC SDM Conference, Norfolk, Virginia, April 7-10, 2003. • Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, "Active authority enhancement of piezoelectric actuator design via mechanical resonance and electrical tailoring", Fifth International Conference on Intelligent Materials (ICIM) June 14 - 17, 2003, State College, Pennsylvania • Jun-Sik Kim, Edward C. Smith and Kon-Well Wang , "Helicopter Vibration Suppression via Multiple Trailing Edge Flaps Controlled by Resonance Actuation System", Tenth International Workshop on Dynamics and Aeroelastic Stability Modeling of Rotorcraft System, November 3-5, 2003, Student Success Center, Georgia Institute of Technology, Atlanta, GA. • Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “High Authority Piezoelectric Actuator Synthesis through Mechanical Resonance and Electrical Tailoring”, Adaptive Structures and Material Systems Symposium, The Winter Annual Meeting of the ASME, November 16 - 21, 2003, Washington Marriott Wardman Park, Washington DC • Jun-Sik Kim, Edward C. Smith and Kon-Well Wang, “Helicopter Vibration Suppression via Multiple Trailing Edge Flaps Controlled by Resonance Actuation System”, the AHS 60th Annual Forum, Baltimore, MD, June 7-10, 2004. • Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “High Authority Piezoelectric Actuator Synthesis through Mechanical Resonance and Electrical Tailoring”, Journal of Intelligent Material Systems and Structures, Vol. 16, No. 1, pp. 21-3, 2005 • Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “Development of a Resonant Actuation System for Active Flap Rotors,” the AHS 61st Annual Forum Gaylord Texas Resort, TX, June 1-3, 2005. • Jun-Sik Kim, Kon-Well Wang and Edward C. Smith, “Design and Analysis of Piezoelectric Transducer Based Resonant Actuation Systems,” Adaptive Structures and Material Systems Symposium, The Winter Annual Meeting of the ASME , November 6-11, 2005,The Walt Disney World Swan & Dolphin Hotel, Orlando, Florida

33. Schedule and Milestones Near Term Mid Term Long Term 2001 2002 2005 2003 2004 Tasks Extension of hybrid analysis to composite rotors, and actuator-circuit model Initial studies on composite rotor and actuators with APPNs Refinement for unsteady aero and control algorithm(dual flap) New actuator concept development and integrated study with rotor Refine aerodynamic model Design, fabrication of actuators Methodology for robust design and adaptive control Refinement and testing of resonance actuation system Development of controller for flap responses in forward flight and investigation of nonlinear features of a RAS

34. Questions? The End

35. Appendix

36. Advance ratio 0.35 Hover Advance ratio 0.15 Operating frequency, 4/rev, 26.6Hz Frequency Responses in Forward Flight Instantaneous frequencies Actuation system w/o circuitry • Influence of advance ratios to the major resonant frequency • Not significant • Averaged frequencies along the azimuth • Almost constant with respect to the advance ratio • RAS can be applied to forward flight as well as hover